Using ants as bioindicators in land management: simplifying assessment of ant community responses.
The indicator qualities of terrestrial invertebrates are widely recognized in the context of detecting ecological change associated with human land use. However, the use of terrestrial invertebrates as biological indicators remains more a topic of scientific discourse than a part of land management practice, largely because their inordinate number, taxonomic challenges and general unfamiliarity make invertebrates too intimidating for most land management agencies. Terrestrial invertebrates will not be widely adopted as biological indicators in land management until simple and efficient protocols have been developed that meet the needs of land managers. In Australia, ants are one group of terrestrial insects that has been commonly adopted as biological indicators in land management, and this study examined the reliability of a simplified ant assessment protocol designed to be within the capacity of a wide range of land managers. Ants had previously been surveyed intensively as part of a comprehensive assessment of biodiversity responses to SO2 emissions from a large copper and lead smelter at Mt Isa in the semi-arid tropics of Queensland, Australia. This intensive ant survey yielded 174 species from 24 genera, and revealed seven key patterns of ant community structure and composition in relation to habitat and SO2 levels. We tested the extent to which a greatly simplified ant assessment was able to reproduce these results. Our simplified assessment was based on ant 'bycatch' from bucket-sized (20-litre) pitfall traps used to sample vertebrates as part of the broader biodiversity survey. We also greatly simplified the sorting of ant morphospecies by considering only large (using a threshold of 4 mm) species, and we reduced sorting time by considering only the presence or absence of species at each site. In this manner, the inclusion of ants in the assessment process required less than 10% of the effort demanded by the intensive ant survey. Our simplified protocol reproduced virtually all the key findings of the intensive survey. This puts effective ant monitoring within the capacity of a wide range of land managers.